540 PHYSIOLOGY CHAP. 



forms intermediate between the erythroblast and the eventual 

 erythrocyte, whereas, on the contrary, every one admits that the 

 transitory forms are rarely met with. The question must, there- 

 fore, be regarded as unsolved. 



Petrone (1898-99) thought he had demonstrated that, while 

 apparently deprived of nuclei, the erythrocytes, when subjected to 

 the action of special reagents, contain a body which has all the 

 cytological and chemical characters of the nucleus. In order to 

 see this it is only necessary to make an extract of living blood 

 with a 1 in 4000 solution of osmic acid. In successful preparations 

 the erythrocytes are seen under the microscope to be in good 

 preservation, perfectly globular (no longer bi-concave), with a 

 homogeneous content. At the centre, or more or less at one side, 

 they exhibit a body with wavy or dentate outline, in which a fine 

 filamentous-granular structure may be detected. This alone stains 



electively with nuclear 



/^^.^ ^flhfev s ^ a ^ ns ' while the rest of the 



\ & x\ /^ H erythrocyte stains with 



/ r ?; V s '3y protoplasmatic dyes (Fig. 



$s x -_>^ 257). According to Petrone 



the supposed nucleus of 

 the circulating erythro- 



/^ /^ . ML cytes is almost always in 



I^B^^H a s ^ e f complete rest, 

 \| although he thinks it pre- 



mature to say that it is 



FIG. 257.- Erythrocytes of healthy man, -showing the entirely lacking in gCI- 



more or less central or excentric corpuscles which minative activitv He 



Petrone holds to be permanent nuclei. From blood . J ' 



immersed in 1:4000 osmic acid, subsequently treated thinKS it probable that 



with baths of picric acid, and then stained with formic ji * r J~ J~ j.u 



haematoxylin and aurantia. thlS depends Upon the 



comparatively short life 



of the erythrocyte, and the predominance of a special iron-carrying 

 haemoglobinogenic function which he attributes to it. 



The work of Negri (1900), however, invalidates Petrone's 

 conclusion that the part of the protoplasm which is shown up by 

 his method of staining can really be interpreted as the nucleus of 

 the erythrocytes. Negri found that this characteristic body can 

 always be demonstrated, on using Petrone's method, in the true- 

 nucleated erythrocytes as well, independent of the nucleus proper, 

 both in the blood of the mammalian embryos and in the blood of 

 such adult animals as normally contain nucleated corpuscles (birds 

 and amphibia). 



IX. Among the lymphoid organs we must also include the 

 Thymus, which consists of a collection of closed follicles, separated 

 by septa or trabeculae of connective tissue. The section of a lobe 

 of the thymus shows under a small magnification a cortical and a 

 medullary substance, which recalls the structure of the lymphatic 



